Field of the Invention
The present invention relates generally to vehicle speed control systems, and more particularly to vacuum actuated vehicle speed control systems.
In the automotive industry, the objective of an automatic vehicle speed control system is to sustain a steady speed under varying road conditions, thus providing the vehicle operator with relief from constant throttle manipulation by the foot. In some cases, the cruise control system may actually improve fuel efficiency by limiting throttle excursions to small steps. Some speed control programs check the vehicle speed in order to determine when to return to set point speed as well as determine when to protect for unsafe acceleration under certain conditions. These systems are ineffective, however, in promptly responding to load increases due largely to the requirement for significant deviation from set speed before correction takes place.
Many vehicles utilize a vacuum actuated speed control servo system for automatic speed control. When a vehicle powertrain including an engine and a transmission is operated under heavy loads and speed control is engaged, the engine""s reservoir vacuum will frequently become depleted and render the system unable to control the vehicle speed as desired. This depletion results in insufficient vacuum in the reservoir to pull the throttle body further open as needed to maintain vehicle speed. Loss of vacuum under high load conditions therefore results in loss of vehicle speed and insufficient force to cause the throttle to achieve a position to initiate a downshift. Current systems fail to adequately address this phenomenon when controlling vehicle speed. The resulting effect experienced by the driver is a significant loss of vehicle speed on inclines or under towing conditions when operating the vehicle in speed control mode. Another problem is associated with the fact that there is difficulty in addressing customer complaints regarding such problems with speed control operation. Simply put, service personnel are often unaware of recent depletions in reservoir vacuum when the vehicle is brought in for maintenance, and may therefore have difficulty diagnosing the problem. It is thus desirable to develop a method and system wherein losses of reservoir volume can be controlled during occurrence and identified during servicing.
The present invention detects a low speed control reservoir vacuum condition and recharges the reservoir vacuum to eliminate the low vacuum condition. This adjustment allows the vehicle to avoid significant deviations from set speed during speed control operation. The low vacuum condition is detected by monitoring various vehicle control signals currently well known in the art. For example, a low/medium throttle angle, combined with a low vehicle acceleration and a high deviation from set speed under certain circumstances can imply that a low vacuum condition has occurred. Thus, by monitoring the vehicle signals for throttle angle, vehicle acceleration, and vehicle speed, the present invention can initiate the necessary downshift to recharge the reservoir vacuum. The present invention also allows for an informational fault to be set in addressing customer complaints regarding speed control operation.
Furthermore, the present invention allows the transmission to return to normal operation either when the low vacuum condition has been eliminated or when a driver override condition is present.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood however that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.